Test if a string contains a substring I have the code file="JetConst_reco_allconst_4j2t.png" if [[ $file == *_gen_* ]]; then echo "True" else echo "False" fi I test if `file` contains "gen". The output is "False". Nice! The problem is when I substitute "gen" with a variable `testseq`: file="JetConst_reco_allconst_4j2t.png" testseq="gen" if [[ $file == *_$testseq_* ]]; then echo "True" else echo "False" fi Now the output is "True". How could it be? How to fix the problem?

You need to interpolate the `$testseq` variable with one of the following ways:

* `$file == *_"$testseq"_*` (here `$testseq` considered as a fixed string)

* `$file == *_${testseq}_*` (here `$testseq` considered as a pattern).




Or the `_` immediately after the variable's name will be taken as part of the variable's name (it's a valid character in a variable name).